“Epidural anesthesia” is one of the most used treatments in regional anesthesia, such as epidural, lower-body operation and post-operative pain control. According to the estimation, the usage of the epidural anesthesia is around 10% of anesthesia now so that there are million cases per year in the world. Taking epidural as an example, there are around 40000 cases in Taiwan every year. For fat patients or the patients with structural spinal abnormalities, operating the epidural anesthesia will be harder as well as the requirements of a positioning needle will be also higher.
The anesthesia of the epidural space uses an epidural needle to penetrate through skin, muscle and ligamentum flavum (LF) for entering into the epidural space in the patient lower back or chest back. A catheter is placed inside and then anesthetics are injected for temporary blocking spinal nerve conduction to reduce the discomfort caused during surgery or post surgery. The epidural space is located between the ligamentum flavum and the dura mater and has a thickness around 2-7 mm. However, the epidural needle insertion is traditionally a blind technique whose success depends upon the experience of the operator. The failure rate of such an operation is around 1-3% and causes complications, such as acute headache.
In clinical, a method of loss of resistance, air or hanging-drop is performed in the epidural anesthesia for placing the epidural space catheter. That is, the operator will feel the loss of resistance after the needle tip goes through the ligamentum flavum for recognizing a position of the needle tip. When the needle penetrates through the ligamentum flavum of the patient, the needle, which is continuously pressed, will enter into the cavity due to the loss of the resistance of air or water for determining if the needle tip is located inside the epidural space. However, this method is not objective and depends on the experiences of operators.
Therefore, the palpation is still a main stream in the operation of the epidural anesthesia and depends on the experiences of the operator. Although pluralities of methods are provided in the prior art, several disadvantages are listed as the following table.
MethodDisadvantagesHigh-frequency ultrasound1. Ultrasound pulser/receiver has angletransducerlimit.2. Resolution is not great.Two-wavelength fiber-optics1. The epidural space distance└cannotbe predicted.2. There is no direct image.Optical fibers for spectroscopy1. The epidural space distance└cannotbe predicted.2. There is no direct image.Time-domain OCT1. There is no direct image.